I think the reason behind it is because everytime you modify a Servlet, you've to recompile your .java Servlet into a .class file. That operation may take some time. When you modify a .jsp page, which in turn makes a call to a servlet, that servlet is already compiled (into a .class).
I could be wrong though. Anyway, I have noticed the same delay as you do (although, not as long as 10-15 seconds, more like 5) whereas jsp is a snap.
Depending how long your tomcat takes to start, it might be a better solution to restart the server every time you modify a Class/Servlet.
I am not sure if you are using an IDE, but I would gladly recommend you Eclipse WTP. With the right plugins, you will be able to start/stop Tomcat from within the IDE and test intensively your code before deploying it. It will also help you with other things, such as registering a new Servlet at your web.xml file on the fly. Eclipse WTP will certainly save you a lot of time ^_^. I can give a hand with the plugins and stuff if you need...
Last edited by Mega Man X; 04-28-2006 at 08:25 PM.